Data encryption in the program

To encrypt data using the common key and the key encrypted for each user password. Thus, each password allows access to encrypted data and componentace one password does not affect the rest parole. However, encrypted data can be compromise, having any of the passwords.

To divide your data into General and private. The key to the shared data stored in the private data of each usara, and the private key data generated based on the password of the user.

>>The user's password will be the private key on the basis of which will be used to encrypt data.
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Clarification.
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The private key is the term asymmetric cryptography. The password cannot be the private key. There are 2 main algorithm of asymmetric cryptography: RSA and DSA (DSA is, for elliptic curves, ECDSA). In one of them you can't use the password as the private key.
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Although... I now came upon a great idea is to generate p and q (all the time the same) password, then don't need to store the private key. Went to think this thought...

And store all passwords in one place (a database, for example)?